Definition 14 (See [1]}) 

A concept class \(\mathcal {H}\subseteq [k]^\mathcal {X}\)  on a Polish space \(\mathcal {X}\)  is
said to be measurable if there is a Polish space \(\Theta \)  and Borel-measurable map \(h : \Theta \times \mathcal {X}\rightarrow [k]\) 
so that \(\mathcal {H}= \lbrace  h(\theta , \cdot ) : \theta \in \Theta \rbrace \) .

